Gas ionization display device

ABSTRACT

A gas ionization display device is provided which comprises a woven wire mesh having noncontacting intersecting wires in hermetically sealed dielectric panels. An inert ionizable gas is encapsulated between the hermetically sealed panels. The device is made by sandwiching the woven wire mesh between two glass panels, with the wires extending beyond the edges of the panels, and sealing the panels, in an atmosphere of an ionizing gas, e.g. neon or argon.

United States Patent Robert E. Bonnet Murray Hill, NJ.

Dec. 22, 1969 Aug. 31, 1971 Engelhard Minerals 8: Chemicals CompanyInventor App]. No. Filed Patented Assignee GAS IONIZATION DISPLAY DEVICE6 Claims, 2 Drawing Figs.

US. 313/ 109.5, 313/203, 313/217, 313/268 Int. Cl H0lj 61/64 FieldofSearch 313/109.5, 210, 203, 268, 217, 108; 315/169 TV, 167, 337

References Cited UNITED STATES PATENTS 7/1937 Brion et a1. 315/337 X2,925,525 2/1960 Davis 313/108 X 3,013,182 12/1961 Russell 313/108 X3,043,988 7/1962 Hurvitzm. 313/108 X 3,278,784 10/1966 Masaharu....313/108 3,497,751 2/1970 Cullis,.1r 313/109.5

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. DemeoAttorneys-Miriam W. Leff and Samuel Kahn ABSTRACT: A gas ionizationdisplay device is provided which comprises a woven wire mesh havingnoncontacting intersecting wires in hermetically sealed dielectricpanels. An

inert ionizable gas is encapsulated between the hermetically sealedpanels. The device is made by sandwiching the woven wire mesh betweentwo glass panels, with the wires extending beyond the edges of thepanels, and sealing the panels, in an atmosphere of an ionizing gas,e.g. neon or argon.

PATENTED M1631 l9?! 3.602756 INVENTOR.

ROBERT E. BONNET GAS IONIZATION DISPLAY DEVICE BACKGROUND OF THEINVENTION This invention relates to a gas ionization display device forproviding illuminated patterns on a transparent panel and to a method offabricating, such device.

Readout devices which provide a visual presentation of storedinformation are required in many forms of modern electronic equipment.The stored data is displayed on a panel in illuminated form in ways wellknown in the art.

Recently illuminated readout panels have been developed which utilizeillumination derived from gas ionization as a means of displaying thedesired information on a flat glass surface. These devices, which arereferred to as plasma display panels, use glass panels separated by agas-filled narrow gap, e.g. about mils wide. The inner opposite faces oftwo glass panels are fitted with a series of parallel conduits, e.g.wires or thin metal strips, and these panels are positioned so that theseries of electrical conductors of the two faces are normal to eachother. Contacts lead out from every conductor and the glass panels aresealed around the edges of the glass. By applying a proper voltage to aset of coordinate conductors, that is strips or wires which have acommon intersection, a glow will appear at the intersection. These glowsor dots form the display pattern, and by proper selection of theconductors in both plates the patterns may appear in the fonn ofnumbers, letters, words, graphs, or figures, as desired. In operationthe devices are maintained at a sustaining voltage and to turn on anindividual spot only a surge in the voltage of the magnitude to initiatean ionization discharge is necessary. Thereafter the glow is maintainedat the sustaining voltage until the voltage is lowered to an eraselevel. The voltages required are a function of the gas, the gaspressure, and the gap between the electrical conductors, and themetallic nature of the surface of the electrical conductors, as is wellknown in the art. If the electrical impulses are computer controlledswitching of a whole display can be achieved in milliseconds.

Many problems have been encountered in the fabrication of these devices.They are difficult to assemble, and it is hard to maintain the gapbetween the closely spaced electrical conductors. Moreover it has beendifficult to provide suitable conductors and/or contacts extending fromthe conductors in the sealed assemblies. l-leretofore some of thedevices have been provided with thin metal films, e.g. by vapordeposition, as the conductors. The problems in forming on the dielectricmaterials thin metal films of sufficient thickness for good electricalcapacity and also good adherence are well known. If the film is toothick it tends to peel and if it is too thin the current carryingcapability is limited. Another method of providing the conducting stripshas been to position wires by potting in the dielectric panels. Thistechnique has not been satisfactory since it has been difiicult toposition and maintain the wires accurately, especially when the wiresare closely spaced. Not only are the labor costs high for this highlyexacting work, but the resulting devices are limited in both size andthe number of wires per inch that can be made by this method. It will beappreciated that the clarity of the pattern is directly related to thespacing of the wire. By increasing the number of wires per inch, abetter resolution of the illuminated pattern can be achieved.

In the present invention a plasma display device is provided which iseasy to assemble and which permits the use of larger panels and agreater number of wires per inch than previously known devices in thisfield.

THE INVENTION In accordance with this invention a gas ionization devicehaving a confined inert ionization gas to display information and havinga first and second set of electrical conductors substantially at rightangles to each other, each set consisting of a plurality ofsubstantially parallel wires, is provided, which comprises: twodielectric panels, at least one of which permits transmission of visibleradiation of gaseous discharge, said panels being hermetically sealed toeach other and having a pocket therebetween; a woven wire mesh havingnoncontacting intersecting wires which form the first and second set ofconductors, said woven wire mesh being sandwiched between the dielectricpanels and having the wires thereof extending beyond the panels andthereby available as electrical contacts;

and an inert ionizable gas encapsulated in said pocket between I thepanels, said encapsulated gas and said noncontacting wires at theintersection sites forming a plurality of closely spaced discrete gasionization points in the device.

The woven wire mesh is made of a fine gauze metal, e.g. about 0.001 to0.050 inch diameter, which is a good electrical conductor. Suitableconducting metals are well known in the art and they include such metalsas copper, silver, Nichrome, and various alloys such as Kovar which havebeen specially developed for making good glass-to-metal seals. It willbe noted that the wire mesh must be sealed in the panels with wiresextending beyond the edges of the sealed panels, and the seal must beleaktight. One method of insuring that there is no leakage at the wiresis to use a metal of the type that is wet by the material of which thepanel is made and has a coefi'lcient of expansion which matches that ofthe panel. However, alternative techniques for forming leaktight sealsare well known in the art.

As indicated previously the wires of the wire mesh do not contact eachother at the cross over points, i.e. the intersections. In a preferredembodiment either the woof or the warp wires are coated with a thinelectrical insulation coating which maintains a uniform gap orseparation between the intersecting wires. The coating is of suitablepenneability for the gaseous environment within the panels. Although itis possible to have both the woof and warp wires coated with anelectrical insulation material, it is not preferred to do so since thisis unnecessary to maintain the gap The electrical insulation coating ispreferably a fibrous or porous material, e.g. fiberglass or asbestos,for the reason that it provides the nonconducting separation between thewires without substantially changing the discharge voltage requirementsrequired for a gap of similar size without the insulation. Organicinsulation material, generally, should be avoided since it tends tocarbonize if heated and this may short the wires. Alternatively, the gapmay be provided by crimping the wires so that they do not contact eachother at the intersections. This crimping is not preferred since it ismore difiicult to maintain the uniformity in the gap throughout themesh.

The inert ionizable gas in the pocket between the panels may be, forexample, neon, argon, xenon, krypton, and mixtures thereof. Such gas iscontained between the panels at a pressure capable of sustaining aglowdischarge.

The encapsulating hermetically sealed panels are made of a dielectricmaterial, at least one of the panels permitting transmission of avisible radiation of the gaseous discharge. Preferably, one of thepanels is transparent. Glass is a preferred material, but othermaterials such as quartz, ceramics, and certain plastics may be used.

It will be appreciated that the operation of the device and thematerials of construction, including the ionizing gas are themselveswell known in the field of gas ionization or neon" lighting as well asin the field of display devices, and the materials and operation of thedevice can be chosen accordingly.

In accordance with another aspect of this invention, the above'describeddisplay device is fabricated by a method comprising, sandwiching thewoven wire mesh between two dielectric panels with the wires of the meshextending beyond the panels, and sealing the panels in an atmosphere ofan inert ionizing gas.

Sealing can be achieved with some materials such as glass by heating tothe softening point in the ionizing gas atmosphere to form a hermetic,or gastight seal around the edges of the panels with an inert ionizinggas entrapped therein. The extending wires are used as electricalcontacts.

Alternative methods of sealing may be used. For example, if thedielectric panels are made of high temperature ceramics, quartz, orunlike materials which cannot be sealed practically by just heating,suitable sealants may be used to obtain a leaktight envelope for themesh. For example, glass frit or thermosetting resins may be used, inaccordance with well-known procedures.

In operation a sustaining voltage is continuously applied in the mesh.When a higher discharge voltage is applied to two wires normal to eachother, a glow point will occur at the intersection thereof. Acombination of applied voltages produces an array of lights which formthe desired pattern. A dropped voltage erases a light. The operation ofthe devices can be computer controlled. As indicated above, suchoperation is well known in the art.

The present device is an improvement over the art in that the devicesare relatively simple to assemble and known techniques such as thoseused to make safety glass can be applied. Moreover, there is no sizelimitation on the woven wire mesh, other than what is required formechanical handling and bonding. In addition, the number of points ofintersection in a given area is only limited by the diameter of thewires. This allows a greater number of points per square inch than hasbeen possible hitherto with the methods of the prior art.

The accompanying figures are provided to aid in the understanding ofthis invention:

FIG. 1 is a schematic plan view of a plasma display device in accordancewith this invention; and

FIG. 2 is a cross-sectional view taken along lines 2-2 FIG. 1.

In FIG. 1 the woven wire mesh in the schematic view shows the warp wires11 and woof wires 12 which are normal to each other, spaced-apart in anexaggerated fashion for better understanding of the configuration. Inthis embodiment of the invention the wires 11 are bare and each of thewires 12 are coated with a porous electrical insulation material 13. Thewires 1 1, and 12 are 2.0 mil dia., and the insulation material isfiberglass and of a thickness of about 1.0 mils. The total diameter ofthe wire 12 and the insulation 13 is 4.0 mils. The wire mesh 10 may befor example 100 mesh.

The pocket 14 formed between the two panels 15 and 16 is filled with aninert gas (not shown), e.g. neon, at a pressure of, for example, 0.33atm.

As shown in the view of FIG. 2, the wire mesh 10 and pocket 14 areencased in transparent panels 15 and 16, e.g. of Pyrex 7740 glass. Thewires 11 and 12 extend freely beyond the panels and are available aselectrical contacts for connection to an outside source of electricity(not shown).

The transparent dielectric panels 15 and 16 are hermetically sealed toeach other around their peripheral edges so that the inert gas isencapsulated in the free space, i.e. pocket 14 therebetween.

EXAMPLE A 100 mesh screen is woven using a standard procedure. Thescreen consists of 0.002 inches diameter bare Kovar wire in the x planeand 0.004 inches diameter porous fiber glasscovered Kovar wire in the y"plane. The fiberglass cover of the wire in the y" plane is0.001 inchesthick, the Kovar wire diameter is 0.002 inches.

To construct a 6 inch X 6 inch display matrix, a screen is cut to a size9 inches X 9 inches. For a distance of 1% inches on the right and leftside of the screen, all of the y" wires are removed leaving only the .r"wires. A similar procedure is followed for the top and bottom of thescreen, only this time removing 1% inches of the x" wires and leavingthe y wires. The fiberglass is stripped from the ends of the y wires fora length of 1% inches, within )6 inches of where the last "x" wire wasremoved. Remaining is the 6 inches M6 inches original mesh bordered by1% inches of bare Kovar wires on two opposing sides and 1% inches bareKovar wires on the top and bottom.

Two pieces of /4 inches thick Pyrex glass are cut to a 7% inches X 7%inches dimension. The prepared screen is then centered on one of theglass plates and the other glass plate is placed over it. Thissandwich-type assembly is than placed in an oven with a weight restingon the top plate. The oven is evacuated, repressurized with pure neongas to about 0.5 atmospheres and the assembly is heated to the softeningpoint of the Pyrex glass, approximately 830 C.

When the glass softens, the neon gas is trapped in the area of thescreen. The sofiened edges of the glass plates bond together forming aseal of approximately A inches in width over the bare Kovar wires on allfour sides, thereby creating a leakproof envelope around the preparedscreen, with the wire ends protruding 5'4 inches beyond the glasssurface. The oven is cooled, completing the formation of the displaymatrix.

Operation of the display matrix requires resistors of 27,000 ohms to beattached to each of the x wires to limit the current to about 12milliamps. A voltage of approximately 270 volts AC is applied to all ofthe x and y" wires. This voltage is not enough to cause ionization. Whenthe voltage is pulsed to 300 volts AC in one of the x" wires and acorresponding y wire, the neon gas at the intersection becomes ionizedand a glow appears. This occurs at the cross outer point of any x and ywire so pulsed. Ionization is maintained by the 270 volts AC. Removingthis holding voltage from the x, y" connections, extinguishes the glowat the ionized intersections.

I claim:

1. A display device having a confined inert'ionizable gas to displayinformation and having a first and second set of electrical conductorssubstantially at right angles to each other, each set consisting of aplurality of substantially parallel wires which comprises:

a. two dielectric panels, at least one of which permits transmission ofvisible radiation of gaseous discharge, said panels being hermeticallysealed to each other and having a pocket therebetween;

b. a woven wire mesh having noncontacting intersecting wires which formthe first and second set of conductors, said woven wire mesh beingsandwiched between the dielectric panels and having the wires thereofextending beyond the panels and thereby available as electricalcontacts;

c. a coating of thin electrical insulation material on at least one setof electrical conductors in the woven wire mesh sandwiched between thepanels; and

d. an inert ionizable gas encapsulated in said pocket between thepanels, said encapsulated gas and said noncontacting wires at theintersection sites forming a plurality of closely spaced discrete gasionization points in the device.

2. A device in accordance with claim 1 wherein at least one of thepanels is transparent.

3. A device in accordance with claim 2 wherein the transparent panel isglass.

4. A device in accordance with claim 1 wherein the thin electricalinsulation coating is gas permeable.

5. A device in accordance with claim 4 wherein the gas permeableinsulation is fiberglass or asbestos.

6. A device in accordance with claim 5 wherein the woven wire mesh ismade of a metal wire which is wet by the panels and has substantiallythe same coefficient of expansion as the panels.

2. A device in accordance with claim 1 wherein at least one of thepanels is transparent.
 3. A device in accordance with claim 2 whereinthe transparent panel is glass.
 4. A device in accordance with claim 1wherein the thin electrical insulation coating is gas permeable.
 5. Adevice in accordance with claim 4 wherein the gas permeable insulationis fiberglass or asbestos.
 6. A device in accordance with claim 5wherein the woven wire mesh is made of a metal wire which is wet by thepanels and has substantially the same coefficient of expansion as thepanels.